The invention relates to a battery cell for a battery, especially for a traction battery, comprising a casing box that is open at one side and a casing cover that closes off the open side of the casing box in a fluid-tight way as well as comprising an electrode plate pack arranged within the casing box that is provided with a terminal that is passed through an opening provided within the casing cover.
Battery cells of the aforementioned kind, on the one hand, and traction batteries that comprise a plurality of battery cells electrically connected to each other, on the other hand, are well known in the prior art so that supporting documentation by printed publications is not required in this context.
As non-stationary batteries, traction batteries are typically employed in automotive technology, for example, in forklifts, elevating trucks and the like. Known traction batteries comprise a plurality of battery cells that are electrically connected to each other. Typically, 12 cells (for 24 V), 24 cells (for 48 V) or 40 cells (for 80 V) are employed as a function of the desired output voltage.
In this context, each battery cell comprises a cell housing that provides a casing box; the casing box, on the one hand, contains an electrolyte as well as alternatingly arranged positive and negative electrode plates, on the other hand, that together create an electrode plate pack. In the final mounted state, the open casing box side of the cell housing is closed off by a casing cover so as to be electrolyte-tight.
For electric connection and/or contacting of the battery cell, terminals are provided which originate at the electrode plate pack and are passed through cover openings provided within the casing cover. In this context, for the purpose of an electrolyte-tight lead-through of the terminals through the cover openings, the cover openings are provided with a soft-elastic sealing sleeve which, in the final mounted state, contacts and rests on the exterior of the respective terminal. Accordingly, a sealing action between the casing cover, on the one hand, and the terminals, on the other hand, is realized as a result of the sealing sleeves, wherein each terminal is provided with a sealing sleeve.
Even though the afore described construction has proven successful in day-to-day practical use, it has its disadvantages; in particular, the sealing action between sealing sleeve, on the one hand, and the associated terminal, on the other hand, is not satisfactory over the course of time. This is so because the geometric dimensions of the individual components, in particular of the terminals, of the casing cover, and of the terminal passages provided therein, have tolerances caused by the production process and therefore can vary. For example, even though the spacing between the terminals provided by the electrode plate pack is predetermined, it varies however. sometimes by a few millimeters; in the final mounted state, this may lead to sections of the terminals being forced more strongly against the respective surrounding sealing sleeve while other terminal sections are less strongly pushed against the respective associated sealing sleeve so that different sealing effects relative to the circumferential diameter of a terminal are generated. Moreover, the terminals also can be oriented such that they are displaced relative to each other like skew lines; this may also lead to non-uniform contacting of the respective sealing sleeve on the associated terminal. This also may cause undesirable leakages already after only a very short period of use of the battery cell.
One more thing has to be taken into consideration in this context. As an electrolyte, sulfuric acid is typically used, in particular in case of lead acid batteries. In this context, there is a particular problem in that sulfuric acid is characterized by a relatively great capillary action so that the electrolyte over time will pass even through smallest cracks and gaps. Possible imprecision in regard to the contacting action of the sealing sleeve on the associated terminal therefore compounds the problem of leakage.
In the prior art further configurations are known. For example, U.S. Pat. No. 6,312,852 B1 discloses a battery with a cover that is provided with monolithic, integrally formed sleeves for the purpose of providing a passage for the terminals therethrough. In this context, the sleeves are embodied with formation of a flexible connection so as to be movable relative to the actual casing cover. In the final mounted state, the sleeves each receive a connector bushing that is either embedded within the sleeve or, with intermediate positioning of a potted epoxide resin, is connected with the sleeve.
WO 90/05999 concerns a passage for a terminal that is characterized by several sealing elements. In this context, a union nut is employed which forces the sealing elements against the respective sealing surface interacting therewith.
GB 2 026 761 A1 concerns a method for producing a terminal post lead-through for batteries. According to this method, a terminal post is embedded in a body of thermoplastic material that subsequently is annularly welded to the cover of the battery. As a welding method, a mirror (hot plate) welding process is used wherein the cover is simultaneously fused to the housing and the body.
DE 25 14 508 concerns a terminal post sealing device according to which a sealing ring and an insulating and compression sleeve are arranged on a terminal post shaft. Moreover, a terminal nut is provided by means of which the insulating sleeve and the sealing ring are tightly pressed onto the terminal post base. The insulating sleeve is positioned in such a way that with its sealing area it is always located below the electrolyte level within the battery cell.
Based on the afore described, it is the object of the invention to provide a battery cell that provides, due to its construction, an improved sealing action between the casing cover and the terminal.